private static void HookUpDefWindowProc(IntPtr hwnd) { SecurityHelper.DemandUnmanagedCode(); #if LOGGING LogFinishHWND(hwnd, "Core HookUpDWP"); #endif IntPtr result = IntPtr.Zero; // We've already cleaned up, return immediately. if (hwnd == IntPtr.Zero) { return; } IntPtr defWindowProc = GetDefWindowProcAddress(hwnd); if (defWindowProc != IntPtr.Zero) { try { result = UnsafeNativeMethods.SetWindowLong(new HandleRef(null, hwnd), NativeMethods.GWL_WNDPROC, defWindowProc); } catch (System.ComponentModel.Win32Exception e) { // We failed to change the window proc. Now what? if (e.NativeErrorCode != 1400) // ERROR_INVALID_WINDOW_HANDLE { // For debugging purposes, throw an exception so we can debug // this and know if it's possible to call SetWindowLong on // the wrong thread. throw; } } if (result != IntPtr.Zero) { UnsafeNativeMethods.PostMessage(new HandleRef(null, hwnd), WindowMessage.WM_CLOSE, IntPtr.Zero, IntPtr.Zero); } } }